Designers of turbines such as those employed in vehicular and aircraft power plants have observed that high operating efficiencies are generally associated with high operating temperatures, because of the greater energy levels of high temperature gases. Internal temperatures of modern turbine engines may typically exceed 1500.degree. F., for example. Moreover, the increased efficiencies potentially obtainable at even higher temperatures have not been realized, largely because of limitations in the properties of materials in current use. Because of the deleterious effects of high temperature gases upon structural components, the use of a variety of metallic and non-metallic materials have been considered, including the ceramics, tungsten alloys, and more recently, carbonized composites.
Whereas ceramic materials are known to be capable of sustaining very high temperatures in certain applications, they tend to be deficient in toughness and resistance to fracture under high stress and vibrational loads. In addition, they are subject to failures, particularly during extended use, when subjected to rapid temperature variances, and to localized thermal shock entailing differing temperatures within an integral component.
Carbonized composite materials are currently being employed in certain aerospace structures which sustain substantial mechanical and thermal stress. Typical applications include the leading edge portions of space craft which are exposed to high temperatures and stresses during reentry. Such composite materials typically include a fibrous component, e.g., fibrous boron or graphite, in a matrix of a thermosetting polymer material, such as a phenolic. Processes for their manufacture typically entail the formation of an uncured workpiece substantially of the configuration desired for the structure, normally with a large proportion of the fibrous components substantially aligned with the axes subject to greatest stress. The workpiece is cured under a prescribed time/temperature/pressure cycle and then pyrolized under higher temperatures to form a high strength carbonized structure, having both fibrous and matrix components in the carbonized state. The cured workpiece, or substrate, may then be coated with an oxidation resistance coating typically containing silicon carbide and silicon metal. Such coated carbon-carbon materials have been demonstrated to maintain structural integrity when exposed to temperatures in excess of 2000.degree. F. and have substantially greater structural strength and toughness than most ceramic structures. Additionally, they may be selectively reinforced to enhance resistance to stress loads along particular axes, as suggested above, and at particular regions, by appropriate orientation and configuration of the fibrous reinforcing material prior to curing.
The commercial manufacture of such composite structures is difficult, however, if parts of complex structural configuration are entailed. For example, whereas multi-bladed turbine rotors of complex configuration may be formed readily of various metal alloys by techniques well known in the art, the manufacture of a carbonized composite rotor having a plurality of blades or buckets and having the capability of sustaining extremely high circumferential and vibrational loads entails substantial technical difficulty. The rotational elements of gas-driven turbine aircraft engines may be driven at rotational velocities exceeding 50,000 revolutions per minute. If formed as a composite structure, lay-up of the fibrous components of such a multi-bladed turbine rotor is difficult because of the structural discontinuities alongside and at the periphery of the rotor, and because of the angular projection of the blades from the plane of the rotor disc. Under the substantial structural loads entailed at high rotational velocities, together with the vibrational cyclical thermal stresses, such multi-surfaces, bladed components are susceptible to distortion and structural failure, and the blades may tend to be broken away from the central disc. In contrast, a rotatable composite disc having an integral, continuous peripheral region (one not divided into multiple blades or buckets) may be more effectively reinforced and manufactured for sustaining the circumferential loads entailed even at very high temperatures and rotational velocities.
A turbine-pump apparatus developed by Nikola Tesla, disclosed in U.S. Pat. Nos. 1,061,206 and 1,061,142, incorporates a rotor structure having a plurality of non-bladed rotor discs mounted coaxially on a rotatable shaft in mutually spaced, parallel alignment. As will be understood more fully from the description hereinbelow of the present system, such "Tesla turbines" and pumps make use of forces derived from surface reactive forces, i.e., forces related to the reaction of a fluid against asperities on the surfaces of the discs, and from surface tension forces related to viscosity of the fluid, i.e., from adhesion of the fluid to the disc surfaces. Thus, fluid injected tangentially into a Tesla turbine apparatus between the discs reacts with the disc surfaces, because of surface tension and reactive impelling forces, to drive the discs in the direction of flow. The teachings of the Tesla U.S. Pat. Nos. 1,060,206 and 1,061,142 are hereby incorporated by reference.
As disclosed in the U.S. Pat. No. 1,061,142 patent, such rotatable, multiple disc structures are also operable as fluid pumps. When the discs are rotated by means of an external motor, fluid is ejected by the discs through a fluid outlet aligned tangentially with the discs. Inlets are provided in the housing communicating through the central regions of the discs, as disclosed in the U.S. Pat. No. 1,061,142 patent. Thus, while the discussion herein will be directed largely to an improved, gas driven turbine, it will be apparent from the description and from the teachings of the U.S. Pat. No. 1,061,142 patent that such power translation apparatus may also be operated as fluid pumping devices.
Although such Tesla power translation apparatus have in fact been employed in certain industrial applications, they are not commonly used in modern gas driven turbines. As will be understood from the description hereinbelow of the operation of the present system, propulsive gasses of substantial temperatures and mass flow rates are preferably employed to drive such turbine apparatus. Because of the high flow energy and operating temperatures, conventional, metal components are susceptible to rapid deformation and deterioration when used in the preferred embodiment of the invention. Furthermore, conventional Tesla turbine configurations (as exemplified in U.S. Pat. No. 1,051,206) are undesirably inefficient with respect to energy transfer and aerodynamic flow. In such configurations, as the inflowing gaseous mixture enters the generally cylindrical chamber in which the multiple discs are rotatably mounted, flowing from an inlet duct along a tangential axis toward the discs, the flow is permitted to expand within an enlarged inlet throat, and subsequently within an annular, circumferential manifold cavity or ramp as it merges with the interior disc chamber and gradually merges with and flows between the discs along a spiral path. Because the gases under high pressure passing through such an inlet throat or chamber are permitted to expand, they lose potential energy while increasing in turbulence, and they subsequently further increase in turbulence as they enter the spaces between the discs. Energy is therefore dissipated by the expansion of the gases within the throat and manifold chambers prior to reaction of the gases with the discs. As the turbulent gases strike the peripheral edges of the discs they are divided and enter the multiple annular spaces defined intermediate the mutually adjacent discs. Further flow inefficiencies result as the expanding gases react turbulently with the peripheral edges of the discs and enter the intermediate spaces.
Conventional Tesla turbine apparatus are further undesirably inefficient when the velocity of the propulsive gaseous flow is required to be varied from a narrow, optimal range. That is, they suffer from an undesirable, substantial decrease in efficiency when the flow velocity of the propulsive gases falls below a given optimal range, related to the diameter and spacing of the discs and the respective areas of the inlet and outlet openings.
Thus, inefficiencies result in conventional Tesla turbines from the loss of energy experienced when the inflowing gases are permitted to expand in an inlet throat upstream of the disc chamber, when the turbulently expanding gases strike the disc edges, and because of the inefficiencies entailed during operational regimes other than a full-power mode, in which the gaseous flow rate is "tuned" to the particular rotor and housing. The Tesla turbine and pump apparatus has not been practicalle for use in modern gas-driven turbine engines or high temperature pumps.